Viruses and Their Properties

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Questions and Answers

What is the primary role of a virus within a host cell?

To reproduce itself by forcing the host cell to create copies (correct)

To carry out cellular respiration

To provide nutrients to the host cell

To help the host cell divide

Which statement accurately describes the virion?

It consists only of RNA.

It is a complete virus particle that may exist in an extracellular state. (correct)

It is not viewed under an electron microscope.

It can reproduce independently of living cells.

During which state does a virus exist only as nucleic acid?

Viral replication state

Intracellular state (correct)

Extracellular state

Virotherapy state

What potential benefit does virotherapy offer?

It reprograms viruses to treat diseases. Signup and view all the answers

What role do viruses play in evolution?

They transfer genes between bacteria and other organisms. Signup and view all the answers

What is the primary component of all virions?

Nucleic acid and protein coat Signup and view all the answers

Which of the following accurately describes viral envelopes?

Derived from host cell membranes Signup and view all the answers

What role do capsids play in viruses?

Protection and transfer of genetic material Signup and view all the answers

Which method is not used by viruses to enter host cells?

Cell division Signup and view all the answers

What determines the host range of a virus?

Receptor availability on host cells Signup and view all the answers

During the assembly stage of viral multiplication, where can some viruses be assembled?

In the cytoplasm or nucleus Signup and view all the answers

What type of genome can a virus possess?

Circular or segmented forms of DNA or RNA Signup and view all the answers

How do nonenveloped viruses typically release from host cells?

By lysing the host cell Signup and view all the answers

Which of the following statements is true about virion enzymes?

Some virions possess enzymes essential for replication Signup and view all the answers

What kind of proteins may project from the surface of a viral envelope?

Envelope proteins as spikes or peplomers Signup and view all the answers

Study Notes

Viruses

Viruses are biological agents reproducing inside living host cells.
When a host cell is infected by a virus, it's forced to produce many identical copies of the original virus.
Viruses are a major cause of diseases.
Virotherapy, using biotechnology to manipulate viruses, is a potential new treatment approach.
Viruses can be used to treat diseases by reprogramming them to combat infectious diseases.
Emerging viruses, like SARS-CoV-2 (COVID-19) and H1N1, pose significant threats.
Viruses play a role in evolution by transferring genes between bacteria and other organisms.

General Properties of Viruses

Virion is the complete virus particle.
It consists of at least one molecule of DNA or RNA enclosed in a protein coat.
Some virions have additional layers.
They can only be viewed with an electron microscope.
Viruses cannot reproduce or divide independently of living cells but can exist outside cells.

Intracellular and Extracellular Viral Form

Viruses exist in two forms: intracellular and extracellular.
The extracellular state is called a virion. This is the form of a virus before entering a host cell.
In the intracellular state, the virus exists as only nucleic acid (genetic material) after entering a host cell. The protein coat is removed in this state.

Virions Infect All Cell Types

Viruses infect all types of cells, including bacteria (bacteriophages).
Most viruses infect eukaryotic cells, including plants, animals, protists, and fungi.
Viruses are classified based on genome structure, life cycle, morphology, and genetic relationships.

The Structure of Viruses

Virus size ranges from ~10-400 nanometers in diameter.
Most viruses need an electron microscope to be seen.
All virions contain a nucleocapsid, composed of nucleic acid (DNA or RNA) and a protein coat (capsid).
Some viruses contain only the nucleocapsid, others have additional components.
These can be enveloped or non-enveloped.

Viral Shapes and Sizes

Viruses exhibit diverse shapes and sizes, depending on the type of virus.
Different images show various virus shapes and comparative sizes of objects.

Capsids

Capsids are large macromolecular structures serving as the protein coat of a virus.
They protect viral genetic material and aid in its transfer between host cells.
Capsids are made of protein subunits called protomers.
Capsids can be helical, icosahedral, or complex in structure.

Viral Envelopes and Enzymes

Many viruses are surrounded by an outer, flexible, membranous layer called the envelope.
Animal virus envelopes often originate from host-cell plasma or nuclear membranes, being composed of lipids and carbohydrates.

Viral Envelope Proteins

Envelope proteins, encoded by the virus, may project from the envelope surface as spikes or peplomers.
These proteins are often involved in viral attachment to host cells, e.g., hemagglutinin in influenza virus.
They can be used to identify the virus.
Some can exhibit enzymatic or other activities; for instance, neuraminidase.
Some may also be involved in nucleic acid replication.

Virion Enzymes

It was once mistakenly believed that all viruses lacked enzymes.
Now it's known that many viruses have enzymes, some associated with the envelope or capsid, and most are within the viral capsid.

Viral Genome

Viral genomes are diverse.
Viruses may have single- or double-stranded DNA or RNA.
Genome length varies between viruses.
Viral genomes can be segmented or circular.

Viral Multiplication

Viral multiplication mechanisms depend on the virus's structure and genome.
Steps involved are very similar for different kinds of viruses. Mechanisms include attachment, entry, genome uncoating, synthesis, assembly, and release from the host cell.

Attachment (Adsorption)

Viruses attach to host cells via specific receptor attachment.
The receptor determines host preference (tissue tropism).
A single host cell can have more than one receptor.
Viral entry can happen with the aid of lipid rafts.

Viral Entry and Uncoating

Viral entry involves either the entire genome or the nucleocapsid, depending on the virus type.
Naked and enveloped viruses are different.
Three methods of viral entry include fusion of the viral envelope with the host membrane, endocytosis into a vesicle, or direct nucleic acid injection.

Synthesis Stage

Viral genome dictates the synthesis processes, based on whether it's DNA or RNA.
ds DNA viruses typically follow typical pathways.
RNA viruses must carry or synthesize proteins needed for the synthesis steps to occur.

Assembly

Late proteins are important for the assembly process.
Assembly is complicated but varies by virus.
Some viruses assemble within the host cell's nucleus.
Others assemble in the cytoplasm.
Viral assembly products can form paracrystalline structures within the host cell.

Virion Release

Non-enveloped viruses lyse the host cell to release new viruses.
Enveloped viruses use budding, where viral proteins are inserted into the host cell membrane, a nucleocapsid binds to viral proteins, and envelopes are derived from the host cell, possibly Golgi or other cellular membranes. Viruses can also use host cell actin to release themselves from infected host cells.

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Description

This quiz explores the fundamental concepts of viruses, including their biological structure, reproduction, and role in disease. You will learn about virions, virotherapy, and the impact of emerging viruses like COVID-19. Dive into the fascinating world of viruses and their significance in both health and evolution.